Generally, in a manufacturing process for a semiconductor device, various processes such as an etching process and a film forming process is performed on a processing target substrate by generating plasma of a processing gas within a processing vessel of a plasma processing apparatus. For example, a parallel plate type plasma processing apparatus is configured to supply a processing gas into a processing vessel and apply a high frequency power to either one of an upper electrode and a lower electrode, which are provided within the processing vessel, from a high frequency power supply. As a result, plasma of the processing gas is generated in a high frequency electric field formed between an upper electrode and a lower electrode.
Further, in the parallel plate type plasma processing apparatus, a matching device is provided between the high frequency power supply and the electrode, and a high frequency power outputted from the matching device is supplied to the electrode via a power transmission line. In the parallel plate type plasma processing apparatus, by providing this matching device, an input impedance of the electrode and an output impedance of the high frequency power supply can be matched with each other, so that the plasma can be efficiently generated within the processing vessel.
A plasma state generated in the plate type plasma processing apparatus depends on electrical parameters such as a load impedance and a power, a voltage and an electric current of a high frequency power supplied to an electrode. Accordingly, if these electrical parameters are calculated and control parameters of the plasma processing apparatus are adjusted based on the electrical parameters, the plasma state can be optimized and stabilized. A plasma processing apparatus capable of calculating the electrical parameters is described in, for example, Patent Document 1.
The plasma processing apparatus described in Patent Document 1 includes a power feed rod that connects a lower electrode and a matching device; and a probe detector fastened to the power feed rod. In this plasma processing apparatus, the aforementioned electrical parameters are calculated by analyzing, through an analyzing unit, measurement signals obtained by measuring an electric current and a voltage in the power feed rod with the probe detector.
More specifically, in the plasma processing apparatus described in Patent Document 1, a high frequency power is continuously supplied from a high frequency power supply to the lower electrode. Further, detection values (i.e., sampled digital values) are obtained by continuously sampling the measurement signals of the electric current, the voltage and the like at a regular cycle.
Meanwhile, in the parallel plate type plasma processing apparatus, a high frequency power in a pulse shape may be applied to the lower electrode. That is, by turning the high frequency power ON and OFF alternately, supply of the high frequency power to the lower electrode and stop of the supply thereof are switched alternately. For example, by stopping the supply of the high frequency power to the lower electrode, a plasma sheath on a processing target substrate is extinguished, and by applying a negative voltage to the upper electrode, negative ions or electrons are supplied to the processing target substrate, so that electric charges of the processing target substrate can be neutralized. As a result, it is possible to allow positive ions to be straightly moved in a subsequent etching process for the processing target substrate.